Beat butter and sugar at medium speed with an electric mixer until creamy. Add egg and almond extract; beat until smooth. Combine flour and salt in a separate bowl; add to butter mixture, stirring until a soft dough forms. Divide dough in half; wrap in plastic wrap and chill one hour.
Roll dough to 1/4-inch thickness on a lightly floured surface. Use alphabet cookie cutters to cut out "happy birthday" cookies; place on greased baking sheets. Bake at 350 degrees for 8 to 10 minutes; cool on wire racks with wax paper underneath racks. Spoon Icing over letters and top with colored sprinkles.